Electrographic printers use a toner station and related processes for mixing and delivering the developer or toner used during the printing process. The term “electrographic printer,” is intended to encompass electrophotographic printers and copiers that employ dry toner developed on an electrophotographic receiver element. The electrographic apparatus often incorporates an electromagnetic brush station, to develop the toner to a substrate (an imaging/photoconductive member bearing a latent image), after which the applied toner is transferred onto a sheet and fused thereon. Related prior art can be found in U.S. Pat. Nos. 4,473,029 and 4,546,060, and U.S. Patent Application Nos. 2002/0168200 and 2003/0091921.
U.S. Pat. Nos. 6,526,247 and 6,589,703 and U.S. Patent Application Publication Nos. 2002/0168200; 2003/0091921; and 2003/0175053 provide additional description of magnetic brush technology using a rotating magnetic core for use in electrographic development apparatus. An essential feature of magnetic brush technology using a rotating magnetic core is that the magnetic field in the development zone has a rotating magnetic field vector. U.S. Pat. Nos. 6,526,247 and 6,589,703 and United States Patent Application Publication Nos. 2002/0168200; 2003/0091921; and 2003/0175053 are hereby incorporated by reference as if fully set forth herein.
U.S. Pat. Nos. 4,473,029; 4,546,060; and 4,602,863 provide a description of magnetic brush technology using a rotating magnetic core for use in electrographic development apparatus. U.S. Pat. Nos. 4,473,029; 4,546,060, and 4,602,863, and U.S. Patent Application Publication Numbers 2002/0168200 and 2003/0091921 are hereby incorporated by reference as if fully set forth herein.
U.S. Pat. No. 5,400,124 provides a description of magnetic brush technology using a rotating magnetic core and a stationary toning shell for applying toner to an electrostatic image. U.S. Pat. No. 5,966,576 provides a description of an alternate configuration of toning station also having rotating magnetic field vectors, in which a plurality of rotatable magnets are located adjacent to the underside of the development surface of the applicator sleeve to move developer material through the development zone. U.S. Pat. No. 5,376,492 discusses development using a rotating magnetic core and an AC developer bias. U.S. Pat. Nos. 5,400,124; 5,966,576; and 5,376,492 are hereby full incorporated by reference as if fully set forth herein.
U.S. Pat. No. 5,307,124 discusses pre-charging toner before feeding into the developer sump containing partially depleted two-component developer material. U.S. Pat. No. 5,506,372 discusses a development station having a particle removal device for removing aged magnetic carrier to compensate for the addition of fresh carrier.
Depositing multiple layers of toner on a substrate by direct deposition from a magnetic brush includes U.S. Pat. Nos. 5,001,028 and 5,394,230, which discuss a process for producing two or more toner images in a single frame or area of an image member using two or more magnetic brush development stations with rotating magnetic cores. In this process, a region of an electrostatic receiver is developed with a first toner of a first polarity and then the receiver with a deposit of charged toner particles is passed through a second magnetic brush using a second toner of the first polarity, which deposits the second toner on the receiver. U.S. Pat. Nos. 5,409,791; 5,489,975; and 5,985,499 discuss a process for developing an electrostatic image on an image member already containing a loose dry first toner image with a second toner having the same electrical polarity as the first toner, using rotating magnetic core technology and AC projection toning, where the developer nap is not in contact with the receiver. U.S. Pat. Nos. 5,307,124; 5,506,372; 5,001,028; 5,394,230; 5,409,791; 5,489,975; and 5,985,499 are hereby incorporated by reference as if fully set forth herein.
For depositing multiple layers of toner on a substrate by transfer of the toner from an intermediate transfer member, intermediate transfer medium, or ITM, U.S. Pat. No. 5,084,735 and U.S. Pat. No. 5,370,961 disclose use of a compliant ITM roller coated by a thick compliant layer and a relatively thin hard overcoat to improve the quality of electrostatic toner transfer from an imaging member to a receiver, as compared to a non-compliant intermediate roller. Additional applications of hard overcoats on intermediate transfer members are disclosed in U.S. Pat. No. 5,728,496 and U.S. Pat. No. 5,807,651, which describe an overcoated photoconductor and overcoated transfer member, U.S. Pat. No. 6,377,772, which describes composite intermediate transfer members, and U.S. Pat. No. 6,393,226, which describes an intermediate transfer member having a stiffening layer. U.S. Pat. Nos. 5,084,735; 5,370,961; 5,728,496: 5,807,651; 6,377,772; and 6,393,226 are hereby incorporated by reference as if fully set forth herein.
U.S. Pat. No. 6,608,641 describes a printer for printing color toner images on a receiver member of any of a variety of textures. The printer has a number of electrophotographic image-forming modules arranged in tandem (see for example, Tombs, U.S. Pat. No. 6,184,911). These include a plurality of imaging subsystems to form a colored toner image that is transferred to a receiver member, the transfer of toner images from each of the modules forming a color print on the receiver member which is fused to form a desired color print. U.S. Pat. Nos. 6,608,641 and 6,184,911 are hereby incorporated by reference as if fully set forth herein. Such a printer includes two or more single-color image forming stations or modules arranged in tandem and an insulating transport web for moving receiver members such as paper sheets through the image forming stations, wherein a single-color toner image is transferred from an image carrier, i.e., a photoconductor (PC) or an intermediate transfer member (ITM), to a receiver held electrostatically or mechanically to the transport web, and the single-color toner images from each of the two or more single-color image forming stations are successively laid down one upon the other to produce a plural or multicolor toner image on the receiver.
As is well known, a toner image may be formed on a photoconductor by the sequential steps of uniformly charging the photoconductor surface in a charging station using a corona charger, exposing the charged photoconductor to a pattern of light in an exposure station to form a latent electrostatic image, and toning the latent electrostatic image in a development station to form a toner image on the photoconductor surface. The toner image may then be transferred in a transfer station directly to a receiver, e.g., a paper sheet, or it may first be transferred to an ITM and subsequently transferred to the receiver. The toned receiver is then moved to a fusing station where the toner image is fused to the receiver by heat and/or pressure.
In a digital electrophotographic copier or printer, a uniformly charged photoconductor surface may be exposed pixel by pixel using an electro-optical exposure device comprising light emitting diodes, such as for example described by Y. S. Ng et al., Imaging Science and Technology, 47th Annual Conference Proceedings (1994), pp. 622-625.
A widely practiced method of improving toner transfer is by use of so-called surface treated toners. As is well known, surface treated toner particles have adhered to their surfaces sub-micron particles, e.g., of silica, alumina, titania, and the like (so-called surface additives or surface additive particles). Surface treated toners generally have weaker adhesion to a smooth surface than untreated toners, and therefore surface treated toners can be electrostatically transferred more efficiently from a PC or an ITM to another member.
As disclosed in the Rimai et al. patent (U.S. Pat. No. 5,084,735), in the Zaretsky and Gomes patent (U.S. Pat. No. 5,370,961) and in subsequent U.S. Pat. Nos. 5,821,972; 5,948,585; 5,968,656; 6,074,756; 6,377,772; 6,393,226; and 6,608,641, use of a compliant ITM roller coated by a thick compliant layer and a relatively thin hard overcoat improves the quality of electrostatic toner transfer from an imaging member to a receiver, as compared to a non-compliant intermediate roller. U.S. Pat. Nos. 5,084,735; 5,370,961; 5,728,496; 5,807,651; 5,821,972; 5,948,585; 5,968,656; 6,074,756; 6,377,772; 6,393,226; and 6,608,641 are hereby incorporated by reference as if fully set forth herein.
A receiver carrying an unfused toner image may be fused in a fusing station in which a receiver carrying a toner image is passed through a nip formed by a heated compliant fuser roller in pressure contact with a hard pressure roller. Compliant fuser rollers are well known in the art. For example, the Chen et al. patent (U.S. Pat. No. 5,464,698) discloses a toner fuser member having a silicone rubber cushion layer disposed on a metallic core member, and overlying the cushion layer, a layer of a cured fluorocarbon polymer in which is dispersed a particulate filler. Also, in the Chen et al. U.S. Pat. No. 6,224,978 is disclosed an improved compliant fuser roller including three concentric layers, each of which layers includes a particulate filler. Additional fusing means known in the art, such as non-contact fusing using IR radiation, oven fusing, or fusing by vapors may also be used. U.S. Pat. Nos. 5,464,698 and 6,224,978 are hereby incorporated by reference as if fully set forth herein.
U.S. Pat. Nos. 5,339,146; 5,506,671; 5,751,432; and 6,352,806 discuss means of forming overcoats on receivers with charged particles in the context of electrographic imaging. U.S. Pat. No. 5,339,146 uses a fusing surface or belt as an intermediate transfer member. This patent discloses mixing a clear particulate material with a magnetic carrier. The clear particulate material is applied using an applicator consisting of a conventional magnetic brush development device. The applicator, using a rotating magnetic core and/or a rotatable shell, moves the developer mixture through contact with the fusing surface to deposit the particulate material on it. An electrical field is applied between the applicator and belt to assist this application. The fusing belt is preferably a metal belt with a smooth hard surface. U.S. Pat. No. 5,506,671 discloses an electrostatographic printing process for forming one or more colorless toner images in combination with at least one color toner image. At each image-producing station an electrostatic latent image is formed on a rotatable endless surface; toner is deposited on the electrostatic latent image to form a toner image on the rotatable surface, and the toner image is transferred from its corresponding rotatable surface onto the receptor element. U.S. Pat. No. 5,751,432 is directed to glossing selected areas of an imaged substrate and, in particular, to creating xerographic images, portions of which include clear polymer for causing them to exhibit high gloss thereby causing them to be highlighted. The clear toner may be applied to color toner image areas as well as black image areas. Additionally, the clear toner may be applied to non-imaged areas of the substrate. In carrying out the invention, a fifth developer housing is provided in a color image creation apparatus normally including only four developer housings. U.S. Pat. No. 6,352,806 concerns a color image reproduction machine that includes means for forming an additional toner image using clear colorless toner particles, thereby resulting in a uniform gloss of the full-gamut color toner image.
In typical commercial electrostatographic reproduction apparatus (copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photoconductive member having dielectric characteristics (hereinafter referred to as the dielectric support member). Pigmented marking particles are attracted to the latent image charge pattern at a developing station to develop such image on the dielectric support member. A receiver member, such as a sheet of paper, transparency or other medium, is then brought into contact with the dielectric support member, and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric support member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric support member, and the image is fixed (fused) to the receiver member by heat and pressure to form a permanent reproduction thereon.
The process of application of the toner to the photoconductive member is optimized to develop the latent image, and at the same time, minimize the transfer of material to the background or non-image areas. The charge of the image and non-image areas are such that correctly charged toner will be attracted to the image area and repelled from the non-image area. Sometimes, toner particles can become reversed-charged from their normal state, due to incorrect or insufficient dispersion of charging agent, or for other reasons. These reversed charged particles can become imaged to the background area, causing image defects.
In the development process, toning materials are often violently engaged with the photoconductive element in order to develop the latent image. This process can provide a source for airborne toner. This airborne toner can easily collect on surfaces near the development zone. As these deposits collect, they can build up and drop off the neighboring surfaces and be developed onto the photoconductive element.
Sometimes the two-component developer material, including a powder toner and a charge carrier material, can build up on the toner roller and when even small amount of toner build up, the subsequent intermittent release of this debris creates unacceptable printing artifacts. One reason this occurs is because the toner is either the wrong sign or 0 sign (neutral) and this material will show up in none image areas of the print as an artifact. This generates an unacceptable toner artifacts on prints from machines running, for instance, at faster rates or that required a high image quality. This debris release typically causes image defects and can accumulate to an extent that the machine must be shut down to be cleaned. It is therefore an object of the present invention to provide a self-cleaning toning roller device.